polybugger.c

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/user.h>
#include <sys/ptrace.h>

#include "polybugger.h"

/*
 * Use rip instead of the eip register due to the machine being x86 64
 */

long getCurrentInstructionPointer(pid_t pid)
{
	struct user_regs_struct r;
	ptrace(PTRACE_GETREGS, pid, 0, &r);
	return r.rip;
}

// A static function makes sure that it is only visible to the polybugger.c file
static void enableBreakPoint(pid_t pid, breakPoint* bp)
{
	bp->data = ptrace(PTRACE_PEEKTEXT, pid, (void*)bp->address, 0);
	// Write back a value of 0xCC in the lower byte of the instruction to set a break point
	ptrace(PTRACE_POKEDATA, pid, bp->address, (bp->data & ~0xFF) | 0xCC);
}

static void disableBreakPoint(pid_t pid, breakPoint* bp)
{
	long instruction = ptrace(PTRACE_PEEKTEXT, pid, bp->address, 0);
	// Check if there was a breakpoint to begin with
	assert((instruction & 0xFF) == 0xCC);
	ptrace(PTRACE_POKEDATA, pid, bp->address, (instruction & ~0xFF) | (bp->data & 0xFF));
}

breakPoint* createBreakPoint(pid_t pid, void* address)
{
	breakPoint* bp = (breakPoint*)malloc(sizeof(breakPoint));
	bp->address = address;
	enableBreakPoint(pid, bp);
	return bp;
}

void deleteBreakPoint(breakPoint* bp)
{
	free(bp);
}

void continueToBreakPoint(pid_t pid, int* status)
{
	if(ptrace(PTRACE_CONT, pid, 0, 0) < 0)
	{
		perror("ptrace() error");
		exit(EXIT_FAILURE);
	}
	waitpid(pid, status, 0);
}

void freeBreakPoints(breakPoint* bp[], uint8_t breakPointCounter)
{
	for(int i = 0; i < breakPointCounter; i++)
		deleteBreakPoint(bp[i]);
}